The railcar has a plurality of axles each supporting at its opposite ends respective wheels running on the rails. Acceleration and deceleration of the railcar are accomplished by using adhesion, or frictional force, between the wheels and rails. The adhesion varies depending upon conditions such as wear and existence of water and/or dust at the contact surfaces between the wheels and rails. Also, the adhesion may vary with dynamic conditions between the wheels and rails such as slide/slip rate. For example, the adhesion increases with the increase of the slide/slip of the wheel against the rail. The adhesion, on the other hand, begins to decrease once it has exceeded an adhesion limit between the wheels and rails.
Accordingly, an application of a certain amount of braking or accelerating torque to the axles can cause differences in rotational speeds thereof due to the adhesion variation between the wheels and the rails. The axles with excessive slide/slip beyond the adhesion limit may result in a significant decrease in adhesion, which in turn causes further slide/slip of the wheels against the rails. The decrease in adhesion may result in that the wheels with sliding/slipping axles exert insufficient braking or accelerating forces between the wheels and rails.
To overcome this problem, there have been used various railcar controlling operations in which the sliding/slipping is detected and then the braking/accelerating torque for the axles associated with the sliding/slipping is decreased to eliminate the sliding/slipping.
Typically, it can be thought that, in the braking operation the increased rotational speed of the axle causes less sliding of the wheels to the rails while the decreased rotational speed causes more sliding of the wheels, and in the acceleration operation the decreased rotational speed of the axle causes less slipping of the wheels to the rails while the increased rotational speed causes more slipping of the wheels. Therefore, according to the conventional method, an assumption is made that the axle with the maximum rotational speed is not sliding in the braking operation while the axle with the minimum rotational speed is not slipping in the acceleration operation, and the maximum and the minimum rotational speeds are used as references in the determinations of the sliding and slipping in the braking and accelerating operations, respectively, in each of which it is determined that the axle is sliding/slipping if an absolute difference between the reference and the actual rotational speed of the axle is greater than a predetermined threshold.
Various conditions such as weight of railcar, characteristic of the motor/brake, and torque command may impose a limitation on the acceleration of the railcar. Then, conventionally the axle is determined to be sliding or slipping if the absolute rate of acceleration of the axle exceeds a threshold corresponding to the limited acceleration.
As described above, according to the conventional control of the railcar, it is determined that the axle is sliding or slipping if the absolute difference of rotational speed or the absolute rate of acceleration is greater than respective threshold and, if at least one of above conditions is true, the braking or accelerating torque applied to the axle is decreased in corresponding to the absolute rotational speed difference and the absolute acceleration rate difference to reduce the sliding or slipping and thereby to reproduce adhesions between the wheels and the rails.
According to the conventional control, however, the adhesion recovers gradually with the decrease in the speed in the same manner irrespective of whether all of or part of the axles are sliding or slipping, which takes relatively much time to recover the adhesion for each and every axle if all of the axles are sliding or slipping to a certain extent (hereinafter referred to as “synchronous sliding” and “synchronous slipping”.)
JP 61-199401 A discloses a method for detecting of sliding, which comprises providing two thresholds of speed difference and acceleration, and determining that all the axles are sliding if at least one of the speed difference and acceleration of the axle is greater than its first threshold but less than its second threshold for more than a predetermined number of axles and also the speed and the acceleration of each axle are less than respective second thresholds. However, if all of the axles are sliding uniformly and synchronously, the acceleration increases beyond its second threshold while the speed difference remains less than its first threshold. Therefore, the method may be unable to detect the synchronous slide and, as a result, the adhesion is recovered individually for respective axles and then takes much time to complete the adhesion recovering process.
JP 11-70870 A discloses that not only the speed difference and the acceleration of the axle but also a differential value of acceleration is used in the determination of the sliding. This method, however, may not be able to detect the synchronous slide/slip, which means that recovering adhesions for all the axles takes a considerable time.
To solve those problems, the present invention provides railcar control apparatus for detecting synchronous slide/slip of the axles to reduce the slide/slip and a method for detecting synchronous slide/slip of the railcar.